1. Field of the Invention
The present invention relates to a paper feeding device for supplying papers to an image forming apparatus, e.g., a copying machine, printer, facsimile machine and the like.
2. Description of the Related Art
Generally, a paper feeding device is installed into the image forming apparatus for supplying papers to an image forming section of the apparatus.
Recently, there are proposals of paper feeding devices uniquely designed for the purposes of space saving and supplying a large number of papers of small size, e.g., A4 size or letter size, which are more frequently used, as disclosed in Japanese Patent Unexamined Publication Nos. Hei. 6-236085 and 7-121084. In those paper feeding devices, paper cassettes containing papers of small size are juxtaposed while being substantially horizontally aligned.
An example of this type of the paper feeding device is shown in FIG. 5. As shown, paper cassettes 20a and 20b, disposed side by side, are provided with paper feeding mechanisms 21a and 21b, respectively. The paper feeding mechanism 21a (21b) picks up papers sheet by sheet from the associated paper cassette 20a (20b), and feeds them to its associated paper transport path 22 and then to an image forming section, which is located in the upper portion of the image forming apparatus.
Pull-out rails 23 are provided on both sides of the paper cassette 20a (20b), and enables the front loading (pulling out of the paper cassette to the front side of the apparatus) for supplying papers.
The paper feeding mechanism 21a (21b) associated with the paper cassette 20a (20b), as shown in FIG. 6, includes a pick-up roller 31, a feed roller 32 and a retarding roller 33.
The pick-up roller 31 is turned in the direction of an arrow B while being in press-contact with the upper surface of a sheet of the uppermost paper P of a stack of papers stored in the paper cassette, to thereby pick up the paper P and feed it in a paper feeding direction (of an arrow A).
The feed roller 32 and the retarding roller 33 successively receive the papers that are let out by the pick-up roller 31 and feeds the papers sheet by sheet to the paper transport path 22. To this end, the feed roller 32 is turned in the paper feeding direction (of an arrow C) on the paper P. The retarding roller 33, located under the paper P are press-contacted with the feed roller 32, while receiving a rotary torque (as shown in an arrow D), opposite in direction to the rotary torque of the feed roller 32, or a stopping torque.
The axial center of the feed roller 32 and that of the retarding roller 33 lie on a perpendicular line in order to feed the paper P substantially horizontally.
In the above-mentioned paper feeding device, the paper cassettes 20a and 20b are juxtaposed at the equal heights, and provided with the paper feeding mechanisms 21a and 21b, respectively. The combination of the feed roller 32 and the retarding roller 33 of each paper feeding mechanism 21a (21b) is located in a further downstream side of the downstream end of the paper cassette 20a (20b) (when viewed in the paper feeding direction).
Therefore, a space in which the feed roller 32 and the retarding roller 33 are placed must be secured between the paper cassettes 20a and 20b. In other words, the paper cassettes 20a and 20b must be arranged so as to provide a given space enough to receive the feed/retarding roller combination. Thus, the space for securing the feed roller 32 and the retarding roller 33, that is, the space other than the space for securing the papers is present between the paper cassettes 20a and 20b. This space is superfluous, and brings about an adverse effect on the efforts of the space saving.
Another type of the paper feeding device is disclosed in Japanese Patent Unexamined Publication No. Hei. 6-100190. The paper feeding device is designed such that papers contained in the paper cassette located upstream (when viewed in the paper feeding direction) are fed through the downstream paper cassette. Therefore, there is capable of simplifying the paper feeding mechanism for the upstream paper cassette, and eliminated the necessity of the superfluous space. However, in this case, the independent paper supplying from those paper cassettes is impossible. Therefore, during the paper feeding to the image forming section, it is impossible to supply papers to either of the paper cassettes. To supply papers to the paper cassette, the paper supplying operation to the image forming section must be interrupted. This impairs the efficiency of the image forming processing in the image forming apparatus.